Method of improving the conception rate in ewes

ABSTRACT

THE CONCEPTION RATE IN EWES IS IMPROVED BY THE ADMINISTRATION OF A GONADOTROPIN AFTER ONSET OF ESTRUS AND INSEMINATION.

United States Patent M US. Cl. 424-100 8 Claims ABSTRACT OF THEDISCLOSURE The conception rate in ewes is improved by the administrationof a gonadotropin after onset of estrus and insemination.

CROSS-REFERENCE This application is a continuation-in-part applicationof our co-pending application Ser. No. 541,086, filed Apr. 8, 1966.

BACKGROUND OF THE INVENTION Heretofore, sex hormones such as theprogestational agents, including progesterone, chlormadinone (6-chloro-A -17-acetoxy progesterone), and the like, or the estrogenic hormones,including estradiol, estratriol, estrone and the like, have beenemployed to synchronize estrus in female mammals. With the increased useof artificial insemination, the synchronization of estrus in femaledomestic animals, particularly sows, cows and ewes, has received a greatdeal of attention since it is most desirable in actual practice to haveall females in the group come into estrus during a oneor two-day periodso that the technician in charge of the artificial insemination programneed not be in attendance every day during an estrus cycle of theparticular species.

In addition to the broad problem of achieving estrus synchronization ina group of female mammals, there is a special problem with regard toinduction of estrus in female sheep. In many breeds of sheep, the ewesundergo a period of reproductive quiescence during the late winter,spring and summer months. Ewes in such a physiological state arereferred to as anestrus. Thus, with ewes, there is a double problem offinding a hormonal drug to induce reproductive activity and then to findthe same or a different hormonal drug to improve the fertility at thetime of the induced estrus.

In general, when it is desired to synchronize estrus in a large group offemale mammals, it has been common to administer a particularprogestational agent to all members of the group for a predeterminednumber of days. After progestational treatment is stopped, estrus beginsa certain number of days later, depending upon the particular speciesinvolved. When estrus is seen to begin, the cycling females are bred,either by artificial insemination or by letting in the males of thespecies. After a first synchronized breeding period, it is a commonpractice to take all of the females who did not conceive at the firstservice and breed them again during the next estrus period, which willbe synchronized naturally (not by drugs) since a group of females(mammals) will usually remain synchronized for 2. to 3 breeding periodsfollowing an initial synchronization using a progestin. It is, ofcourse, an object of any breeding program, including the type outlinedabove, to achieve the highest possible conception rate after two cycles.However, normally with sheep, conception rates following twosynchronized breeding periods will be in the range of 70 to '80 percent.

3,574,829 Patented Apr. 13, 1971 It is an object of this invention toprovide a method for increasing the pregnancy rate and number of livebirths in ewes by a hormonal treatment initiated after the onset ofestrus.

DESCRIPTION OF THE INVENTION In fulfillment of the above and otherobjects, this invention provides a process for increasing the pregnancyrate and percent of live births in ewes by administering a gonadotropinto said ewe after the onset of estrus. While we prefer to administer thegonadotropin to the ewe also after insemination or impregnation, it ispermissible to administer the hormone before the ewes are bred provided,of course, that insemination occurs while the ova produced duringovulation are still fertile.

We have found, surprisingly, that treatment of a group of ewes afterovulation and breeding with a gonadotropin greatly increases both theconception rate in the group as a whole and also the number of livebirths, as compared to the number of live births in a group of ewesreceiving no gonadotropin after the onset of estrus. While it has been acommon practice to use gonadotropins to induce follicular growth andovulation in female mammals, gonadotropins have not heretofore been usedto increase conception rates after estrus and ovulation in ewes. Theterm gonadotropin as used herein includes, among other preparations,pregnant mares serum (PMS), lutenizing homone ('LH), folliclestimulating hormone (FSH), and human chorionic gonadotropin (HCG).

In carrying out the process of this invention, ewes are administered agonadotropin within 1-16 days following estrus and breeding. Thus, ourinvention comprises the administration of a gonadotropin to an ovulatingfemale mammal after the onset of estrus and during the estrus cycle,said female being bred within a few hours after the onset of standingestrus. More particularly, our invention finds its most beneficial usein an estrus synchronization program specifically employing ewes as thefemale mammal to be so treated. In such a program, a group of cyclingewes is synchronized by treatment for 14 to 16 days with aprogestational agent such as chlormadinone acetate. The drug is thenwithdrawmthe ewes coming into estrus during the next dive days. As soonas signs of estrus show, each ewe is artificially or naturallyinseminated. One to 16 days later, during which time about to percent ofthe ewes have come into heat, and have been bred, a gonadotropin such asPMS or HCG or a combination thereof is administered to each member ofthe group. The conception rate of those ewes receiving the gonadotropinsis increased 12 to 26 percent by this treatment and the number of lambsper ewe lambing is increased 18 to 50 percent. This same regimen isemployed in the anestrus non-cycling ewe, except that prior to theadministration of PMS or HCG to increase conception rate and to increasethe number of lambs born per pregnant ewe, an earlier treatment with aprogestine plus PMS must be used to induce follicular growth andinitiate the estrus cycle. In general, the gonadotropins, not beingorally active, are administered by injection.

The following experiments will more fully explain the nature of ourinvention:

Experiment I A group of 73 anestrus ewes were treated with chlormadinoneacetate for 16 days. Each ewe then received an injection of PMS toinduce estrus and ovulation. All of the ewes coming into heat after thePMS injection were inseminated by fertile rams. Twenty-seven of the eweswere then administered PMS 16 days after first com- 0 ing into heat. Thecontrol group of 46 did not receive PMS after breeding. Sixty-threepercent of the ewes in the treated group lambed, whereas only 50 percentof the ewes in the control group lambed, a difference in conception ratein favor of the process of our invention of 26 percent. The treatedgroup had 1.9 live lambs born per pregnant ewe, while the control grouponly had 1.7 live lambs per pregnant ewe.

The over-all results of this experiment are as follows:

TABLE 1 Lambing Over-all N0. of No. of rate, difference, Group eweslambs percent percent Treatment 27 32 118 Control 4e 39 85 +39 1 Percentof treated ewes.

In another similar experiment, a control group of 69 anestrus ewes,which did not receive any PMS after induced ovulation and estrus,yielded only 1.4 live lambs per pregnant ewe and only 48 percent of theewes conceived. In a similar group of 22 ewes treated according to theprocess of this invention, 59 percent of the ewes lambed and 1.9 livelambs were born per pregnant ewe. The over-all results of thisexperiment are as follows:

In this experiment a group of 178 cycling ewes were treated as follows:126 were synchronized by the administration of a progestin(chlormadinone) for a 16-day period, after which the entire group wastreated with PMS or HCG at 24-96 hours, after estrus, ovulation andbreeding. The control group of 52 ewes were synchronized by the samemeans with chlormadinone, but the ewes in this group did not receive anyPMS or HCG following estrus, ovulation and breeding. In this experiment,50.0 percent of the ewes treated with PMS or HCG lambed, but only 42.3percent of the control ewes lambed (a difference of 118% The over-allresults of this experiment are as folows:

1 Percent of treated ewes.

It can be seen from the above experiments that not only does thegonadotropin treatment program involving the process of this inventiongive a 1826 percent higher conception rate, but also it increases thenumber of live births per pregnant ewe by a substantial factor (22% toThe increased birth rate brought about by the process of this inventionis not readily explicable by present day theories of hormonal treatment.By either method-t he double breed cycle with gonadotropic injection orthe one without-the same number of females come into estrus. Thus, theimproved results cannot be attributed to an increased number coming intoestrus and thus ready to conceive. The treatment must, therefore, eitherincrease the conception rate or decrease the fetal death rate or both,by a mechanism that has not been fully explained.

We claim:

1. A method of increasing the pregnancy rate and percent of live birthsin ewes which comprises administering a gonadotropin by injection to anewe after said ewe comes into estrus and is inseminated.

2. The process of claim 1 in which the gonadotropin is administered from1-16 days after onset of estrus.

3. The process of claim 1 in which the gonadotropin is pregnant maresserum.

4. The process of claim 1 in which the gonadotropin is human chorionicgonadotropin.

5. The process of claim 1 in which the gonadotropin is folliclestimulating hormone.

6. The process of claim 1 in which the gonadotropin is lutenizinghormone.

7. The process of claim 1 in which the ewe is bred within a few hoursafter the onset of estrus.

8. In an estrus synchronization program for breeding ewes, theimprovement which comprises administering a gonadotropin by injection toeach of said ewes from 1-16 days following ovulation and insemination.

References Cited Pincus et al.: The Hormones, vol. III, 1955, AcademicPress, New York, N.Y., pp. 337-342.

SAM ROSEN, Primary Examiner US. Cl. X.R.

